Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? State the postulate.

For the retinal cancer retinoblastoma, the inheritance of one mutated copy of RB1 from one of the parents is often referred to as a mutation that produces a 'dominant predisposition to cancer.' This means that the first mutation does not produce cancer but makes it very likely that cancer will develop.

Using RB1⁺ for the normal wild-type allele and RB1⁻ for the mutant allele, identify the genotype of a cell in a retinoblastoma tumor.

Which of Mendel's postulates are illustrated by the pedigree that you constructed in Problem 3? List and define these postulates.

What advantages were provided by Mendel's choice of the garden pea in his experiments?

An organism has alleles R₁ and R₂ on one pair of homologous chromosomes, and it has alleles T₁ and T₂ on another pair. Diagram these pairs of homologs at the end of metaphase I, the end of telophase I, and the end of telophase II, and show how meiosis in this organism produces gametes in expected Mendelian proportions. Assume no crossover between homologous chromosomes.

The following figure shows the results of Mendel's test-cross analysis of independent assortment. In this experiment, he first crossed pure-breeding round, yellow plants to pure-breeding wrinkled, green plants. The round yellow are crossed to pure-breeding wrinkled, green plants. Use chi-square analysis to show that Mendel's results do not differ significantly from those expected.

An experienced goldfish breeder receives two unusual male goldfish. One is black rather than gold, and the other has a single tail fin rather than a split tail fin. The breeder crosses the black male to a female that is gold. All the F₁ are gold. She also crosses the single-finned male to a female with a split tail fin. All the F₁ have a split tail fin. She then crosses the black male to F₁ gold females and, separately, crosses the single-finned male to F₁ split-finned females. The results of the crosses are shown below.

Is black color dominant or recessive? Explain. Is single tail dominant or recessive? Explain.

An experienced goldfish breeder receives two unusual male goldfish. One is black rather than gold, and the other has a single tail fin rather than a split tail fin. The breeder crosses the black male with a female that is gold. All the F₁ are gold. She also crosses the single-finned male to a female with a split tail fin. All the F₁ have a split tail fin. She then crosses the black male to F₁ gold females and, separately, crosses the single-finned male to F₁ split-finned females. The results of the crosses are shown below.

  Black male x F₁ gold female:

    Gold        32

    Black       34

  Single-finned male x F₁ split-finned female:

    Split fin       41

    Single fin    39

What do the results of these crosses suggest about the inheritance of color and tail fin shape in goldfish?

Cytoplasmic male sterility (CMS) in plants has been exploited to produce hybrid seeds. Specific CMS alleles in the mitochondrial genome can be suppressed by specific dominant alleles in the nuclear genome, called Restorer of fertility alleles, RF. Consider the following cross:

♀CMS 1Rf 1/Rf1 rf2/rf2 × ♂CMS2rf 1/rf1 Rf2/Rf2

What genotypes and phenotypes do you expect in the F₁? If some of the F₁ plants are male fertile, what genotypes and phenotypes do you expect in the F₂?